Many current wireless communication systems involve wireless cellular networks. These networks are generally terrestrial radio frequency (RF) networks made up of a number of cells each served by at least one fixed-location transceiver known as a base station. These base stations provide wireless communication links with various mobile devices or user equipment (UE) that pass through the cell served by the particular base station. Advances in terrestrial RF systems have allowed enormous growth and accessibility of wireless voice and data communication to the population and because of the various standardized wireless protocols, the costs for providing such wireless services and UE is relatively low.
One shortcoming of wireless cellular networks is coverage area. In order to maximize the serviceable capacity of any given cell area, the fixed-location base stations are configured to have only a certain, limited range. The limited range allows for reuse of the available channels, which increases the overall capacity of the network. Because a fixed-location base station is used to provide wireless access to the communication system, there can be no service where no base station exists. Moreover, various terrain features, such as trees, mountains, buildings, and the like, can block the RF signals or prohibit installation of the base stations, thus, effectively reducing coverage areas. Therefore, in remote locations, where base stations would be impossible or impracticable to place, a mobile device or UE becomes effectively a paper-weight having complex, but still quite useless electronics while in the no-coverage area.
In order to address some of the coverage limits, personal satellite communication systems have been developed. While satellites have been used in backend or backbone communication transmissions for many years, use for personal communication systems has only more recently been implemented. In such satellite systems, a satellite phone or satellite communication device acts as a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions.
Satellite communication systems experience some of the same shortcomings as terrestrial communication systems, such as signals being blocked by trees, buildings, and the like. However, a satellite communication system can typically provide communication access in extremely remote locations, as long as the location is visible to a certain number of orbiting satellites. Thus, where a terrestrial communication system would typically fail to provide access in the middle of the ocean, or particular dessert or mountain range, a satellite communication system will generally provide communication through signals communicated directly between the UEs and one or more orbiting communication satellites.
While terrestrial wireless communication systems have taken off and become very widespread around the world, satellite communication systems have failed to enjoy similar success likely because of the large initial start up costs for the communication companies to deploy the requisite number of satellites into orbit and, for the user, because of the relatively high costs of the associated mobile devices/UEs, as well as high usage costs, sometimes adding up to several U.S. dollars per minute. However, as wireless technology has advanced, it has become feasible to share mobile hardware for processing both terrestrial and satellite communications. Moreover, hybrid terrestrial-satellite communication systems have been suggested that provide for a mobile phone or UE to use terrestrial base stations when practical, but then switch to satellite stations when the mobile phone or UE is no longer able to reliably couple to the terrestrial base station.
One issue that arises in pure satellite or hybrid terrestrial-satellite systems is adapting the various terrestrial wireless standards to satellite operations. Adaptation of these standards allows more of the same UE technology to be used, “as is,” or with only slight changes in order to be compatible between both the terrestrial and satellite systems. Fewer or no changes equates to lower costs for and higher access to the satellite systems. Problems often arise, however, in adapting the terrestrial standards to satellite operations because satellites are simply much further away from the average user than a typical terrestrial base station. The sheer distance affects satellite signals through signal strength and long roundtrip delays. Weaker signals equate to lower data rates, while roundtrip delays can be up to 500 ms compared to terrestrial roundtrip delay times at less than 20 ms.